@ketz555 Checking the repository that you’ve linked to, I can see that npm run start:backend executes nodemon server.js and the server.js file starts an Express server.
You won’t be able to do this on Netlify, as it’s not how the hosting environment is intended to be used.
The static portion of your application builds via CI and deploys to CDN, and then any runtime server side functions (or API’s) that you integrate with must either be running elsewhere, or be implemented via Serverless functions.